FIG. 1 shows a block diagram of a conventional battery charging circuit 100. As shown in FIG. 1, the battery charging circuit 100 is implemented by an adapter 102, a pulse width modulation controller 108, a charger controller 110, and a battery protection circuit (not shown) in the battery pack 104. The adapter 102 outputs a fixed voltage, and a charger 106 (shown as the pulse width modulation controller 108 and the charger controller 110) steps down the output voltage of the adapter 102 by controlling power switches and a buck converter in block 112. Consequently, conventional battery charging circuits can be relatively large and costly.
FIG. 2 shows a block diagram of another conventional charging circuit 200. The charging circuit 200 includes a controllable adapter 202 and an external control chip shown as a charger controller 210. The external control chip (charger controller 210) controls an output power of the controllable adapter 202 according to a current/voltage of the battery pack 204. As shown in FIG. 2, the charging circuit 200 also needs an extra switch 212 to control a charging current of the battery pack 204. As a result, such battery charging circuits are also relatively large and costly.
In conventional charging circuits such as the charging circuit 100 and 200, due to unbalancing issues (e.g., cells in the battery pack may have different voltages/capacities), some cells may reach an over-voltage condition even though others have not yet been fully charged. Although a cell balancing circuit can be used to relieve cells from such unbalancing issues, cell balancing is typically enabled only when the battery is nearly fully charged, in order to avoid excessive heat generation. As a result of the limited balancing time, the cell balancing circuit may not be effective. In other words, the charging process is not accurate enough across all of the cells.
Battery packs are also used in electric vehicles. Electric vehicles use one or more electric motors for propulsion. The motors can draw the electric power from the battery pack to drive the wheels or propellers. The electric vehicle can be equipped with a battery charging circuit which transfers energy from a conventional power outlet or a dedicated charging station to charge the battery pack. The battery pack in an electric vehicle includes a relatively great number of battery cells coupled in series, e.g., more than 100 cells, which increases the complexity of the wire connections among different cells. In addition, the conventional charging circuit, e.g., the charging circuit 100 or 200, may not fully charge all of the cells during a charging process. Thus, the lifetime of the battery back in the electric vehicle may be shortened, thereby decreasing the power efficiency of the battery back.